Aircraft landing wheel shimmy damper



Dec. 8, 1953 B. E. OCONNOR ETAL AIRCRAFT LANDING WHEEL SHIMMY DAMPER 2 Sheets-Sheet 1 Filed Dec. 11, 1950 Ben amin Faezze v pkg/9.1

Patented Dec. 8, 1953 mt omxiMicm n.

A pplicat'ionhecembenl1, 15150;-SerialrN o; 2110;218{

The present invention" relatestozimprovements; viscous: fluid shimmy dampers: eSp,ecialltf adaptedi for preventing shimmy swlvel ngc-orv casterstype aircraft landingvwheeli assemblies;

It is: an important: object of'thez present; in mention: to provide a simplified iecnnornicali shimmy ciamperwinstal lati'ornifor aircrafit; land; ing wheels on similar; swiveling. or caster-type: mechanisms whenein'; due-.toj various f-actcrs frequency: vibrationsor oscillations; may develop I in" service and which. itizis' highly desirable} t9;v

dampen; i

A- further object of; the: invention is to. pro; vid'ean. improved shimmy damper: installation; which. is especially useful: in con-junction; with the torque scissorsi ofra'acasteri wheel landing, stm-itaircraft Qtlier-objects, featuresamt advantages of the. present inventien will be readily apnarent; fr ei7 r i; the: following detailed description.- of, certain preferr'ed embodiments thereof? taken in; (191 111 1 6:- tion with the accompanying drawings, in which-1' Figure 1 is afragmentary near; elevational view of a swivel-type aircraft landing. gear strut; structure showing the present. invention applied thereto; a

Figure 2 is aside elevationalfvi'ewotthelangh ing-gear' strut-shown in Figs :1

Figure: 3 is a top" plan: view of the shimmy; damper used." in the installation of Fig; 1 and.

4' Claims. (01. 2414 -19411 mper assembly l5 is pr.oy ide d. lihisidampe p is of av king; that} has] a working amnlituglel of 69 s as? erm t i-ullw swiveling o l e Wheel; about; the axisof. thecyl-inder I2; Further-mane tatably; unbn. the strut la. nd is. operatively' c n; nected to the yoke ll through the medi nn: 011a,

endofthefih; ted.-pivota la efiwee osses a 26 provided therefor on the wheel yoke H' an 1 V the cortesponding inner end: of the, link lagis with certain partsicroken. away 'andiirr. sectinn ,1

to reveal details of'structure:

Figure 4 an enlargedi fragmentarw data; sectional view" taken substantially on the line IV -IV- of Fig; 2.;

Figure 5' is abottom: plan view. of a; modified? form of the damper; and

Figure 6 is a partially elevational' and partially sectional detail view taken substantial-1 p on: the,

irregular line: VI'VI'of Fig; 5. r

I'n'a swiveling or caster-type aircraft land ingwheel assembly such. as: shown in; Figs}. 11' and 2 the carriage comprises an oleo strut. N: attached non-rotatably to the: aircraft (not shown) andaswivel m of wheel: yoke? lgi which carries the stud shaft providing the wheel axle (not shown). A swivel connection between-the: yoke I I and the strut proper: I20 is efiiectedyby' means of an upwardly piiojecting cylinclen I22; which is rotatably aniyertically reciprocably; engage'ct within a tubular casing k3; of; the: rut including bearing structure'- (Fig a therein for the cylinderlL a For damping shimmy-in thewheel-suppmi l-ne gear including theyoka Hz, animprcmedshimmy I Qnnected; pivota s n a olizpntalo x s q' d r necting eats 0 13 bosses. 2glfon, the damper a'sg Sa m l5. 'E roushl th s: arransementt caL mov m s w en e m k Mi a d-. h shimm i dampen I 5, as occasioned, byoperati nof; the strut lit are accommodated hilt neventhe V sen tivecnn fion s a nta n d b we wheely k andth h m d mpe it W11 i thus he appa zentfthat thefdam-perl5; provides, n fi c a: rotary lip r ns'c ec ib TQ tomlleseissors H with the-strut llll,

lilescriloed. inl' .gene'al terms}. the, sin m5; dampe s; Qt th w erein he qua resist'ance ojf'fsheaitof a. suitable, viscous fluid operating betweenj opposed patalleli Wonk; ng l 3 0Q fl $ilZ Y mb a i ii he res fi iv ,s a ts tel-ledv upon r sistant dampen, Vi-b atoty oscilla ons or s'h mmy- E 'r h s Dune pose, the damper utilizes ayi'scous. fluid; wh h will iunction eff ciently. with substant l'y' fqrmity ouglim an ex r mef anseo te R atune co tions, Fb 'e amnla a silicone fiuidi or, 3Q,QQO, centistokies "viscosity rating. as mcasuigeuf in, a. s ,bolt'jivisc'osimetex ha' "l;QQ1} iound'top oclunee e1len sults,

a m rebri atin 1 b s muc thi r ha willrzesultn a-Tm ie flui flfr tiona i d1 ns l be ween hec m te-"p ra lel suria-ces oi the'damneg and, the, viscous; fl of,

Stat d'-anothf he W l ing; is; tgropeigly 1 correlated .to nuid rtoafibn a; linear veloc H es i edi roma no i'ne velecitsc gra u so to Yprpducgin'the. fluid layer ajcgnfitionl of snsa. 'ratheii' than a "fluid, drag; relatj'o' he the e a ende cy bwaml, rapicl. rela, pata e m -ye nent-efif hewo ki urfa s condition arisesff rorn theiniathematical factthat t loq ty Q a min a to the yeloity oi the the distance from the stationary boundary to the layer in question divided by the distance between boundaries if the proportion of the viscosity to the distance between the boundaries is sufficiently high. This can be shown graphically by a straight diagonal line tilting in the direction of movement of the moving surface to represent linear velocity gradient, and a curving line from the stationary surface to the moving surface to represent non-linear velocity gradient where the surfaces are further apart than will result in a linear velocity gradient when considered with respect to the viscosity of the fluid in question. Thus, while the viscous fluid when in a shear film between opposed relatively parallel moving working surfaces, will allow comparatively free relative parallel movement of the working surfaces during slow relative motion, rapid relative movements are resisted due to the shear resistance of the film of the viscous fluid between the working surfaces.

The novel structure by which the improved results of the present invention are attained in the shimmy damper l comprises an annular housing having shimmy dampen means therein and externally surrounding and rotatable about the strut l0" To this end, the damper housing comprises (Figs. 3 and 4) a cooperative pair of separately formed and functionally integrally united housing members 22 and 23 and a mounting hub rin 24.

The housing member 22 is preferably constructed as an annular flange-like disk element of a thickness consistent with the character of the material from which made to withstand the service usage to which put. At its inner margin the housing member 22 is provided with an axially outwardly projecting annular hub flange 25 providing an internal annular friction bearing surface 21 of substantial width complementary in diameter to the opposing journal bearing external surface of the hub ring 24. At its outer margin the housing member 22 is provided with an integral annular flange 28 extending axially in the opposite direction to the hub flange 25 and defining with the body of the housing member 22 a damper chamber 29. g The remaining housing member 23 is also in the form of an annular flange-like disk element constructed of appropriate material of a thickness suitable to withstand all service usage to which put. Formation of the housing member 23 is such as to make it complementary to the housing member 22 and to serve as a closure plate for the chamber 29. For this purpose the housing member 23 is preferably of somewhat smaller external diameter than the member 22 but of somewhat larger diameter than the outer peripheral diameter of the chamber 29 as defined by the inner periphery of the housing member flange 28, so that the outer margin of the housing member 23 will seat upon a shoulder 30 provided by a rabbet groove at the inner corner of the terminus of the flange 28. Assembly of the housing plate members 22 and 23 is maintained permanently as by welding 3| at the junctureof the outer margin of the housing member 23 and the flange 28. At its inner margin, the housing member 23 has an axially outwardly extending hub bearing flange 32 substantially like the hub bearing flange 25 of the housing'member 22 and providing an internal friction bearing surface 33 of substantial width bearingly engaging the external bearing surface of the hub ring 24.

For practical reasons the damper I5 is preferably constructed as a unit that can be assembled complete at the factory by mass production methods of manufacture ready for assembly with the airplane landing wheel strut I0. Therefore, the bearing hub 24 has means thereon for retaining the chamber-forming housing members 22 and 23 permanently against axial separation from the hub member. By preference such. means comprise a lateral rib or flange 34 formed integrally in one piece with the body of the hub ring 24 and projecting radially from the outer bearing surface of the hub ring. The flange 34 is engaged in slidable bearing relation between the inner margins of the opposed faces of the housing members 22 and 23 and thereby retains the assembled housing members 22 and 23 and the hub ring 24 in predetermined axial relationship.

At its opposite ends, the hub ring 24 projects beyond the respective adjacent ends of the housing member hub bearing flanges 25 and 32, respectively. Thereby, the hub ring 24 is adapted to be mounted in encircling relation about the lower end portion of the strut casing 13 with the upper end of the hub ring engaged against the lower surface of an annular radially extending limit shoulder flange 35 on the casing, while the lower end of the hub ring is engaged by a retaining nut 3'! turned up on a threaded peripheral portion 38 of the strut casing. In this mounted position, the hub ring 24 is held nonrotatably by means of a key 39 fitting in a keyway 40 in the outer periphery of the casing and a complementary keyway 4| in the inner periphery of the hub ring 24. Thus, that portion of the damper housing provided by the housing members 22 and 23 is supported for free rotary but non-axial movement about the hub ring portion 24 of the housing which is held non-axially and non-rotatably movable relative to the strut casing l3.

Within the chamber 29, the casing or housing members 22 and 23 have respective spaced parallel annular working surfaces 42 and 43 which operatively oppose parallel working surfaces of a relatively thin resistance member 44 the thiclmess of which is less to a predetermined extent than the space between the working surfaces 42 and 43 to afford shear films of a viscous coupling, damping fluid between the opposed working surfaces of the housing members and of the resistance member. For example, where a silicone fluid as described hereinabove fllls the chamber 29, the cooperating elements may be so proportioned that the shear film spacing between the opposed cooperating working surfaces will be provided by approximately .010 inch clearance. It has been found that adequate damping accrues from the use of a single resistance member 44 having relatively large working surface area. This enables the damper to be made in a very compact form and quite economically.

The resistance member 44 may be constructed as a simple die stamped substantially ring-shaped plate from material as thin as practicable as will withstand buckling in the presence of the torsional stresses imposed in the operation of the damper as a result of the resistance to shear of the viscous damping fluid.

In order that the resistance diskfor. plate 44 may be self-adjustable for shear film spacing in operation, the plate may be disposed axially loosely but relatively non-rotatably about the hub provided by the hub flange 34. Onthe other hand; resistance plate w mysesa ly secured t tlie- =nange w W-it1i -Th W01kl g surfaces el -tn ate space'd equiiilstantly from the: opposite faces of the: flange m eitner" instance,- asimpl'e and expedient: manner of assembling the-resistant .p1ate'4*- with the flange com-- prises haviug'thefiange ofl nontcireularr outline,

such for example as hexagonal as best seen in Fig. with the inner periphery: of the: plate 4:!

provided: with: a complementary: closely-z fitting edsate. g

A ieitss outer" periphery; th'e resistance: plate at isipreferably fornredz. with: a cylindrical edge 4d whichzconc-entricallyropposessthe inner periphery? ofithe housingzfl'angez2'8iinishear'film spacedxrelatlcni Thereby thetareai ofitl're outer p'eritpii'eryg ofii the: resistance plate: cooperated with the-renn stantializ axially facing} working; surface areas to affiord in the aggregate; larger resistance: area for operation of; the: viscous: damping: coupling-. .v

- Aifiter asscmbly'rof the various damper housing" and: resistance plate: components has. been cons;

ably provided at diametrically opposite sides of thehousing. I

I n-order, to'prevent leakage of therdamping fluid member 62 is predeterm tied to afford: shear fl'l lns ar 'nscous fiureintne sadness I in modified remi or dampen; the res sistance member: 621 is ferment integral one;

piece with 'tlie hub r ng" Te this end the resistance rr iei-nber is formed: as: radial: amin lar" extender-1 on a substantially thicker but-mar---- rowen'shouider'flan e: disposed annularl piece to: projectiradiaily from: the. mid the outer'beariug surface or the hub ring 55;v Thain-her internar margins-m: the housing;menr-- 52": and fl are rabbet groovd as indicated? ta accemmo'date the snoufder flange lie-int slidfigrbearihg relatibn;. I Bearing: engagemenu of the housing members 5-2": and With the hub:- ring 55=-is enacted: by meanest respective. oppositely: axially extending inner marginal bearing flanges: 65 and 69% re sp'ectivelyz. I Sealing rin s 68 supported at the bearingr iaces: of: the flanges 55 and G l revent; leakage etnuiu: thereby: from: the; damp F-hdds me v Viscous:- damping: fluid is filled into the shamhm 54i-v througmappropriatefilling openings 69 which: subsequenttc: fillingofthe: are closed by means of closureplugs' -l'lli 'l h'eda'm per" unit is adapted to-bemounted on wheel: supporting strut similarlyas the damper and the-inner face ofth'ehub ring past-Qthe hub bearing of the housing, eachof' the housing hub-bearingflanges -and 32 is-preferably provid ed with an annular groove 56 within which is accommodated a resilient sealing ring 5i preferably of the O-ring: type formed from. rubber or, synthetic rubber;

The torque scissors linkage connection ears or bosses 2| are preferably provided on the lower housing member 23 and may be formed integrally in one piece therewith, if preferred.

In the modified form of damper [5 shown in Figs. 5 and 6, much the same structural relationships are present as in the damper unit 15. In the modification, housing members 52 and 53 are secured together to define therebetween a working or damper chamber 54 and are mounted upon a hub ring 55 which provides the radially inner closure for the chamber 54 similarly as provided by the cooperative housing components of the damper l5.

The damper housing member 52 is formed of substantial diameter and has an outer marginal axially extending annular flange 51 formed with an inner side terminal edge rabbet groove 58 with in which the outer margin of the housing member 53 is seated. Permanent assembled relation of the housing members 52and 53 is maintained by means of a retaining flange 59 at the extremity of the body flange 51 and which terminal flange is turned over into retaining engagement with the margin of the cover member 53.

The cover members 52 and 53 are provided with inner opposing working surfaces 60 and 6! which oppose parallel respective large area working surfaces on a thin resistance member 62in the form of a disk plate as thin as practicable consistant with service requirements. The clearance between the working surfaces 60 and *6! and the opposing working surfaces of the resistance strut support .me'mber M turns relative to-the' strut l ll 'd uring" 55 n: provided with a keywa'y H: taretain it' nemrotata-bly'onlthestrut. v

Pivotal connection of the upper'linlr'of atorque scissors ilinkage to the damper I5 is adapt ed; to be effected to" attacnmentbosses or cars 1-2: provided: on: the housingmember 53." Bear=-- ihgvbushings: T3 'ma y be press fitted into aligned bearing apertures in'the pivot ears the operation oi tl'ie damper unit- [-5- orthe damper! unit 15 the torquescissors [-1 assures a, coupledv relatio "ship between the wheel-sup portingsmembe and the damper-unit on'the When the wheel-supporting operational maneuvers which involve relatively" slow turning or swiveling of the support or yoke member ll, substantially'negative or zero resistance prevails in the damper unit. However, in the event of high frequency oscillatory or shimmy movements of the Wheel-supporting yoke member H with respect to the strut ID, the resistance to shear of the viscous damping fluid in the damper operating between the parallel working surfaces therein resists, and dissipates or dampens the vibrations and thus prevents shimmy.

It will be apparent that either form of the viscous shimmy damper disclosed comprises a bare minimum of relatively simple and easily manufactured parts that can be produced economically by rapid mass production methods of manufacture and which can be assembled easily and quickly on an assembly line. Moreover, by reason of the few, simple and rugged and durable parts of which the damper is composed, the margin of manufacturing error is greatly reduced so that loss by rejection is greatly minimized. Also, there are no delicate parts that might be subject to damage in service or wearing out, so that the damper can be used indefinitely without replacement or repair.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

ing structure having an annular chamber there-' inof very narrow axial spacing but of substantial diameter, a single resistancev disk stationary with and encircling said member and extending intosaid chamber, the inner faces of the opposite axial walls of the housing structure providing a single pair of opposed working surfaces in parallel spaced relation to the opposing surfaces of said single disk, and a connection externally of said members between the housing structure and the other of said members for rotation of the housing structure with said other member, said chamber having a viscous fluid therein'and said opposed surfaces within the chamber andof said disk being operatively in shear film spacing with respect to the fluid so that rapid relative rotary movements of the housing with respect to said disk are restrained by the shearing action of the fiuidbetween the surfaces of the chamber and the disk.

2. A shimmy damper adapted to be mounted in encircling relation about a member of an airplane wheel supporting structure, said damper comprising a ring hub, said hub having rotatable therewith a radially outwardly directed annular resistance disk of substantial diameter disposed in substantial spaced relation from both ends of the hub and provided with axially oppositely directed faces, and a housing enclosing said disk and rotatably mounted upon said hub at both sides of said disk, said housing having therein a chamber defined by axially facing walls havinginternal surfaces complementary to and opposing said disk faces in respectively closely spaced relation for operative shimmy damping coupling of the opposing surfaces and faces by a damping medium enclosed within the chamber.

3. A shimmy damper according to claim 2 wherein said disk comprises a plate stamped from sheet material and having its inner periphcry of non-circular outline, and the hub has a complementary projectingportion thereon fittin said non-circular inner peripheral outline of the disk to key the disk for rotation with the hub.

4. In combination in a shimmy damper of the character described, a pair of opposed annular housing members of substantial diameter secured together at their outer peripheries in narrow spaced relation, integral respective oppositely directed axially extending bearing flanges on the inner peripheries of said members, a hub ring with which said flanges are in bearing and supported relation, a radially projecting axial positioning flange'of limited thickness on said hub ring spaced substantially from both ends of said hub ring and engaging between the inner margins of said housing members, and a resistance disk of less thickness than said flange projecting radially from said flange into the space between said housing members.

BERNARD E. O'CONNOR. BENJAMIN FUEN'IE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,718,175 Nilson June 18, 1929 2,061,656 Guthrie Nov. 24, 1936 2,339,450 Ashton Jan. 18, 1944 2,356,468 Parker Aug. 22, 1944 2,372,710 Chisholm Apr. 3, 1945 2,393,110 Kops Jan. 15, 1946 2,508,217 Brell May 16, 1950 2,514,137 OConnor July 4, 1950 FOREIGN PATENTS Number Country Date 580,127 Great Britain Aug. 28, 1946 

